MONITORING SURVIVAL AND MOVEMENT PATTERNS OF SEA OTTERS (ENHYDRA LUTRIS KENYONI) IN KACHEMAK BAY, ALASKA AUGUST 2007-APRIL 2010 BY ANGELA M. DOROFF AND ORIANA BADAJOS FINAL REPORT TO: MARINE MAMMALS MANAGEMENT U. S. FISH AND WILDLIFE SERVICE 1011 E. TUDOR ROAD ANCHORAGE, AK 99503 30 JUNE 2010 Kachemak Bay Research Reserve, 95 Sterling Highway Suite 2 Homer, Alaska 99603 TABLE OF CONTENTS LIST OF TABLES ..................................................................................................................................... iii LIST OF FIGURES ................................................................................................................................... iii ABSTRACT ................................................................................................................................................ 1 INTRODUCTION ...................................................................................................................................... 2 METHODS ................................................................................................................................................. 2 RESULTS ................................................................................................................................................... 3 DISCUSSION ............................................................................................................................................. 7 ACKNOWLEDGMENTS .......................................................................................................................... 9 LITERATURE CITED ............................................................................................................................. 10 APPENDIX A ......................................................................................................................................... A-1 APPENDIX B ......................................................................................................................................... B-1 ii LIST OF TABLES Table 1. Capture and tagging information from 44 sea otters which were instrumented with VHF radio transmitters in the intreperitoneal cavity and systematically monitored during 31 July 2007 – 03 May 2010 in Kachemak Bay, Alaska. ................................................................................................................. 4 Table 2. The monitoring results of 44 VHF radio-tagged sea otters for survival and causes of mortality during 31 July 2007 - 01 January 2010 in the Kachemak Bay, Alaska. ..................................................... 6 LIST OF FIGURES Figure 1. The core study area was located in Kachemak Bay, Alaska, and sea otters with VHF radio transmitters were relocated each week by aircraft. Areas outside of the core study area were searched intermittently for missing animals. The remote data logger was set up to identify seasonal habitat use of Mud Bay.................................................................................................................................................... 11 Figure 2. Group sizes at relocation for 44 sea otters with VHF radios (n=2768 high quality relocations). For all sex and age classes combined, the group size most frequently encountered at the time of each relocation was ≤ 20 sea otters. .................................................................................................................. 12 Figure 3. Percentage of sea otters (n=44) in our study which were relocated each month throughout August 2007-April 2010. In 2010, the rate of detection progressively decreased until 66% of the study animals were missing (radio battery expiration was the assumed cause). At the close of the monitoring on 03 May 2010, the status was: 9 alive (20%), 6 dead (14%), and 29 missing (66%). ......................... 13 Figure 4. Cumulative plot of high quality relocations (n=2147) for 32 tagged male otters (2 pups, 16 subadults, 14 adults) from August 2007-April 2010. ............................................................................... 14 Figure 5. Cumulative plot of high quality relocations (n=621) for 12 female tagged otters (4 subadults, 8 adults) from August 2007-April 2010....................................................................................................... 15 Figure 6. Cumulative plot of high quality relocations (n=196) of tagged adult female sea otters with dependent pups from August 2007-April 2010. ....................................................................................... 16 Figure 7. Male otters were rarely found along the south shore of the Bay, with the exception of established territories for males LCI001, LCI027, LCI028, LCI030, LCI033, and LCI036. This figure depicts locations of the tagged males while they were actively territorial (see appendix B for all relocations). ............................................................................................................................................... 17 Figure 8. Cumulative plot of high quality relocations (n=625) for foraging sea otters (high quality ≤ 0.5 km) of all sex and age classes from August 2007-April 2010. ................................................................. 18 iii ABSTRACT Sea otters (Enhydra lutris kenyoni) strand and die for a variety of reasons, including disease, starvation, predation, and trauma. Beginning in 2006, there was an unusually high number of subadult male sea otters dying from Streptococcal endocarditis, encephalitis and/or septicemia, referred to as Strep. syndrome in Kachemak Bay, Alaska. To better understand the progression of the Strep. syndrome in free-ranging sea otters, the U.S. Fish and Wildlife Service implanted VHF radios into 44 sea otters in Kachemak Bay to monitor health, survival, and movements, and to assess causes of mortality. During 31 July 2007 – 03 May 2010, we monitored 12 female (4 subadults, 8 adults) and 32 male (2 pups, 16 subadults, 14 adults) sea otters by aircraft and remote data logger (2008-2010 only). The average period between locations of each study animal was 12 days. By January 2010, the status of the study animals was: 30 alive, 6 dead, and 8 missing. After January 2010, the rate of detection progressively decreased due to the expiration of the battery life of the radio transmitters. We continued to locate study animals to monitor for mortality, and at the close of the monitoring, on 03 May 2010, the status was: 9 alive, 6 dead, and 29 missing. Study animals may be missing (undetected) for a variety of reasons, including radio failure, movement outside the study area, and undetected mortality. Causes of mortality were disease (2 adult females), trauma due to boat strike (1 adult male), and take during subsistence hunting (3 adult males). Both females and the male which died of trauma had forensic level necropsies performed; the female otters showed evidence of Strep. syndrome and the adult male did not. Male and female otters used spatially distinct regions of the Bay, and both sexes appear to have seasonal use patterns. During the monitoring period, all females had at least 1 pup; on average, a pup was born to each female every 1.2 years, indicating ample food resources. At the close of the study, all subadult males were alive, with one (6%) missing, whereas 58% of the female otters were either dead or missing. Carcass collection methods are biased by the habitat used by particular sex and age classes of otters and the areas available to be searched by stranding volunteers. Carcass recovery efforts indicated that subadult male otters were more vulnerable to Strep. syndrome than other sex and age classes, however, this study indicates that reproductive-age female otters may be more vulnerable. The survival of females appears particularly low (50%), however, our sample size was small (n=12). Of the known causes of mortality in our study, 67% are directly human related (boat strike and harvest) in Kachemak Bay. While the overall mortality rate for the Kachemak Bay study area is likely not significant on a broad population level, this study has been informative and elucidates the ease at which unreported and undocumented mortality can occur in this, or likely any other, region within the population range. 1 INTRODUCTION Sea otters (Enhydra lutris kenyoni) strand and die for a variety of reasons, including disease, starvation, and trauma in Alaska. In the Kachemak Bay area, there has been an unusually high number of subadult male sea otters dying from Streptococcal endocarditis, encephalitis and/or septicemia (hereafter referred to as the Strep. syndrome) (Gill et al. in prep). Because Strep. syndrome was the most frequent cause of death for recovered sea otter carcasses in Kachemak Bay, the U.S. Fish and Wildlife Service (FWS) recommended the event be investigated in collaboration with the Unusual Mortality Event (UME) team which is provisioned under the Marine Mammal Protection Act. With a dedicated team of researchers, the FWS implemented several studies to both identify causes of the syndrome and to understand the potential impact to the population. Early findings indicate that most of the isolates in the Strep. syndrome of sea otters in Alaska are Streptoccous infantarius ssp. coli (Burek et al. in prep). The cause of this unusually high occurrence of the disease is unknown. However, there is evidence of a morbillivirus and Bartonella in this population, which could lead to immunosuppression and/or damage to endothelial